172 ANIMAL ACTIVITIES. 
cavity, being careful not to disturb the organs within. 
Do you find the body-cavity ? 
Pass a probe down the mouth until you are able to 
make out the stomach, the cesophagus, extending from 
the mouth to the stomach, and the intestine, extending 
from the stomach to the anal opening. This is the 
alimentary canal. Is the intestine coiled or straight? 
Sketch this alimentary canal. 
Do you find a membrane holding the stomach and 
intestine in place? This is the mesentery. Do you 
see blood-vessels in the mesentery ? 
In the front of the body-cavity do you see the large, 
Fic. 133.—Internal Organs of Fish. @, cesophagus; dca, stomach; /, 
duct of swimming-bladder; 4, swimming-bladder; 4, ovary. 
brownish liver? Can you find a gall-bladder, green 
or yellow in color, attached to the liver ? 
In the body-cavity can you see the reproductive or- 
gans? Usually these are smooth and whitish in the 
male and yellow and granular in the female. 
Directly under the back-bone do you find the air- 
bladder? This organ is homologous with the lungs of 
higher vertebrates. Do you also find a large blood- 
vessel above the air-bladder ? 
Brain and Nerves. Use the head of a large fish 
obtained from the market. With great care remove 
the upper part of the skull. Commonly it is better to 
use preparations previously dissected by the teacher. 
These may be kept in formalin, or alcohol. The 
